The effects of pre/postnatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on various immunological, bone marrow and host susceptibility assays were examined previously in B6C3F1 hybrid mice. These studies were continued with several other compounds including a biphenyl (non-halogenated) chemical, orthophenylphenol. The effects of orthophenylphenol (OPP) and tris(2,3-dichloro-propyl)phosphate (Fyrol FR2) on immunological functions and host susceptibility to infectious agents were examined following subchronic exposure to nontoxic levels in adult mice. Also included in these studies as a positive control were mice treated with cyclophosphamide (CY), a known immunosuppressant and cyto-reductive drug. Exposure to relatively high doses of OPP (up to 200 mg/kg body weight per day for 10 days) failed to alter immune functions or host susceptibility. Fyrol FR2 treatment induced minimal changes in immune functions and host susceptibility only at the highest dose tested (25 mg/kg per day for 4 days) as indicated by decreased lymphoproliferative responses to mitogens and increased tumor takes following tumor cell challenge. In contrast, CY treatment resulted in marked alterations in both immunological functions and host susceptibility.